In this April 19, 2011, file photo, a member of the National Guard checks on his colleague inside a Border Patrol Skybox near the Hidalgo International Bridge in Hidalgo, Texas. An unprecedented surge of children caught trudging through South Texas scrublands or crossing at border ports of entry without their parents has sent government and nonprofit agencies that handle their shelter, legal representation and reunifications scrambling to expand their services.

In this April 19, 2011, file photo, a member of the National Guard checks on his colleague inside a Border Patrol Skybox near the Hidalgo International Bridge in Hidalgo, Texas. An unprecedented surge of

An undated handout photo of a Lackland Air Force Base dormitory being used for children who crossed the border alone. In April, 2012, federal officials began housing 200 illegal immigrant children at the base, turning a vacant dormitory that was once the living quarters of basic training recruits into an emergency shelter for young illegal immigrants. (Office of Public Affairs, Administration for Children and Families via The New York Times) -- EDITORIAL USE ONLY

An undated handout photo of a Lackland Air Force Base dormitory being used for children who crossed the border alone. In April, 2012, federal officials began housing 200 illegal immigrant children at the base,

File - In this June 8, 2011, file photo, U.S. Customs and Border Patrol agents patrol along the Rio Grande near Penitas, Texas. An unprecedented surge of children caught trudging through South Texas scrublands or crossing at border ports of entry without their parents has sent government and nonprofit agencies that handle their shelter, legal representation and reunifications scrambling to expand their services.

File - In this June 8, 2011, file photo, U.S. Customs and Border Patrol agents patrol along the Rio Grande near Penitas, Texas. An unprecedented surge of children caught trudging through South Texas scrublands

A sharp influx of undocumented immigrant children in recent months has severely strained the federal government's capacity to provide them with shelter, leaving hundreds of children sleeping on cots in gymnasiums and in an Air Force dormitory in Texas.

More than 5,200 undocumented children and youths without parents or legal guardians in the U.S. were turned over to the Office of Refugee Resettlement in the first six months of this fiscal year - a 93 percent increase over the same time period last year, according to government data.

Kenneth Wolfe, a spokesman for the resettlement agency, said officials are at a loss to explain the reason for the increase in unaccompanied youths, who typically are held in the government-contracted shelters while their immigration cases are pending, unless the government can find a relative or custodian to take custody of them.

While the number of children and teens in the agency's custody has soared, overall arrests of illegal immigrants have declined to lows not seen since the 1970s, government data shows.

Most of the children are from Guatemala, Honduras and El Salvador, and immigrant advocates who work closely with them said they have not identified significant changes in their reasons for coming to the U.S.

Federal officials have scrambled to find enough beds to accommodate the influx, creating five temporary shelters in Texas, including a dormitory on San Antonio's Lackland Air Force Base that holds 200 children.

The gymnasiums of two shelters for immigrant children in Harlingen also have been used as temporary housing, state records show.

Some immigrant advocates worried that the "surge" shelters may not meet with the stringent requirements outlined in federal law and in a class-action lawsuit from 1985, which set specific, minimum standards for the care of undocumented children and teens.

"When we hit these kinds of numbers, it's important that the standards not slip because we are in triage mode," said Wendy Young, the executive director for Kids in Need of Defense, a nonprofit in Washington, D.C., that matches pro bono attorneys with immigrant children and youths.

In a statement, federal officials said the shelters follow the same guidelines as licensed child care facilities in Texas. The children have their own beds, access to a phone to contact family members, three meals and two snacks daily, onsite medical professionals, showers, restrooms, clean clothes and recreation time, officials said.

Lauren Fisher, a project coordinator with the South Texas Pro Bono Asylum Representation Project, said the temporary shelters cover basic services, but may not offer the same depth of care as in a normal shelter, such as mental health services and education.

"It is a stress to the entire system," Fisher said. "I think everyone is doing what they can to accommodate, but it is certainly not ideal."

Federal officials said they have identified an additional 850 permanent beds that will be available by mid-June, and plan to phase out the temporary shelters by the end of the summer.

BCFS Health and Human Services, a nonprofit organization, has submitted plans with the state for a new facility in Baytown that could add 168 permanent beds.

The organization also is in the process of adding 67 beds to its Harlingen shelter, records show.